title: Auxin distribution is differentially affected by nitrate in roots of two rice cultivars differing in responsiveness to nitrogen.
abstract: OBJECTIVE
  Although ammonium (NH4(+)) is the preferred form of nitrogen over nitrate (NO3(-)) for rice (Oryza sativa), lateral root (LR) growth in roots is enhanced by partial NO3(-) nutrition (PNN). The roles of auxin distribution and polar transport in LR formation in response to localized NO3(-) availability are not known.
  
  
  METHODS
  Time-course studies in a split-root experimental system were used to investigate LR development patterns, auxin distribution, polar auxin transport and expression of auxin transporter genes in LR zones in response to localized PNN in 'Nanguang' and 'Elio' rice cultivars, which show high and low responsiveness to NO3(-), respectively. Patterns of auxin distribution and the effects of polar auxin transport inhibitors were also examined in DR5::GUS transgenic plants.
  
  
  RESULTS
  Initiation of LRs was enhanced by PNN after 7 d cultivation in 'Nanguang' but not in 'Elio'. Auxin concentration in the roots of 'Nanguang' increased by approx. 24 % after 5 d cultivation with PNN compared with NH4(+) as the sole nitrogen source, but no difference was observed in 'Elio'. More auxin flux into the LR zone in 'Nanguang' roots was observed in response to NO3(-) compared with NH4(+) treatment. A greater number of auxin influx and efflux transporter genes showed increased expression in the LR zone in response to PNN in 'Nanguang' than in 'Elio'.
  
  
  CONCLUSIONS
  The results indicate that higher NO3(-) responsiveness is associated with greater auxin accumulation in the LR zone and is strongly related to a higher rate of LR initiation in the cultivar 'Nanguang'.
authors.affiliation: Key Laboratory of Plant Nutrition and Fertilization in Low-Middle Reaches of the Yangtze River, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Song
authors.forename: Huwei
authors.initials: H
authors.lastname: Sun
authors.forename: Jiao
authors.initials: J
authors.lastname: Li
authors.forename: Xianpo
authors.initials: X
authors.lastname: Gong
authors.forename: Shuangjie
authors.initials: S
authors.lastname: Huang
authors.forename: Xudong
authors.initials: X
authors.lastname: Zhu
authors.forename: Yali
authors.initials: Y
authors.lastname: Zhang
authors.forename: Guohua
authors.initials: G
authors.lastname: Xu
mesh_terms: D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D005966:Glucuronidase / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000494:pharmacology*; D012275:Oryza / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000033:anatomy & histology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014316:Tritium / Q000378:metabolism
chemical_list: D007210:Indoleacetic Acids; D009566:Nitrates; D014316:Tritium; D005966:Glucuronidase; D009584:Nitrogen
keywords: Auxin distribution; Oryza sativa; lateral root; nitrate; rice